The present invention relates to slurries for use in chemical mechanical polishing, in particular, the polishing of barrier layers that isolate copper interconnects.
When making advanced semiconductor devices, copper interconnect lines may offer a number of advantages over aluminum-based interconnects. For that reason, those making such devices have turned to copper as the material of choice for making the devices"" interconnects. To minimize unwanted diffusion of copper into other device regions (e.g., adjacent dielectric layers or transistor areas), barrier layers may be formed to insulate copper interconnects from those other regions.
When a single or dual damascene process is used to form a copper interconnect for a semiconductor device, such a barrier layer is deposited onto a dielectric layer to line a trench (or trench and via) that was etched into that layer. In addition to lining the trench, the barrier layer extends across the surface of the dielectric layer. A seed material, e.g., one including copper, is deposited on the barrier layer, followed by performing a conventional copper electroplating process to form a copper layer. Like the barrier layer, excess copper may form on the dielectric layer.
After the barrier and copper layers have been formed on the dielectric layer, excess material (i.e., material deposited outside the trenches) must be removed. A conventional chemical mechanical polishing (xe2x80x9cCMPxe2x80x9d) process is typically used to perform that function. In an example of such a process, a substrate or waferxe2x80x94held by a carrierxe2x80x94is placed face down on a polishing pad that is fixed to a table (sometimes called a platen). The carrier applies a downward pressure on the backside of the substrate as the carrier and platen are rotated. Meanwhile, a slurry is deposited onto the pad as the substrate is polished. A slurry that differs from the one used to remove the excess copper may be used to remove the excess barrier layer material, which is located beneath the copper layer.
Current CMP processes can yield defective devices. When a CMP process removes copper from a barrier layer, it may form a depression within the trench. Such a xe2x80x9cdishingxe2x80x9d effect can give the dielectric layersxe2x80x94subsequently formed on the copperxe2x80x94a similarly shaped indentation where formed above the copper. That indentation results because dielectric layer deposition is, in general, a conformal process. When copper is deposited on those dielectric layers, copper fills that indentation when it fills the trenches. If the subsequent copper CMP step stops on the dielectric layer, copper xe2x80x9cpuddlesxe2x80x9d may remain at the end of that polishing process. If those copper xe2x80x9cpuddlesxe2x80x9d touch adjacent copper lines, those lines could be shorted.
Another problem may arise because of the way slurry composition affects the polish rate for different materials. When certain slurries are used to remove a barrier layer (e.g., one containing tantalum or tantalum nitride) from the surface of a dielectric layerxe2x80x94after excess copper has been removed from the barrier layer""s surface, the barrier and dielectric layers may polish at a faster rate than the remaining copper. As a consequence, the resulting dielectric layer may be recessed below the copper to a significant degree (e.g., greater than about 200 angstroms). At the interface between the dielectric layer and the copper, which fills the trench, an additional localized polished region may form a depression at the edge of the copper layer, which may appear as xe2x80x9cfangs,xe2x80x9d when viewed in cross-section. Such xe2x80x9cfangsxe2x80x9d could exceed 600 angstroms in height.
For certain dielectric layers (e.g., silicon oxyfluoridexe2x80x94hereinafter identified as xe2x80x9cSiOFxe2x80x9d), a slurry may enable copper, and the barrier and dielectric materials, to be polished at similar rates. Using such a slurry may enable dielectric, barrier and copper layers to be polished down to a substantially planar structurexe2x80x94eliminating, or at least reducing, any adverse impact that may result from xe2x80x9cdishing,xe2x80x9d recessed dielectric layers, or xe2x80x9cfangxe2x80x9d like protrusions. When, however, the dielectric layer is made from other types of materials (e.g., a carbon doped oxide, hereinafter identified as xe2x80x9cCDOxe2x80x9d), such a slurry may not cause these materials to polish at similar rates.
Accordingly, there is a need for a new slurry for polishing a barrier layer. There is a need for such a slurry that enables a CMP process to simultaneously remove copper, and barrier and dielectric layer materials, to produce a substantially planar surface. There is also a need for a tunable slurry that enables such materials to be polished at similar rates, even when the dielectric layer is formed from different substances. The present invention provides such a slurry.